1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a method of routing a call directed to a portable directory number in a radio telecommunications network.
2. Description of Related Art
Number portability (service provider portability) allows subscribers to retain their directory numbers (DNs) as the subscribers "port" from one service provider to another. In a radio telecommunications network, when a call is placed to a portable DN, the originating mobile switching center (MSC) must send a query known as a Number Portability Request (NPREQ) to a Number Portability Database (NPDB) to obtain a routing address for that portable DN. However, when the call originates in a MSC that "owns" the DN, sending the NPREQ may not be necessary, and may be a waste of time and system resources. In this case, the MSC should send a routing number query such as a Location Request (LOCREQ) Invoke message to the home location register (HLR) to obtain a routing number. However, there is currently no process by which the MSC may give priority to one of the two queries (LOCREQ or NPREQ), or salvage a call if the chosen query does not return a useful result.
In order to overcome this disadvantage, it would be advantageous to have a method of prioritizing the LOCREQ and NPREQ queries, and salvaging a call if the chosen query does not return a useful result. The present invention provides such a method.